The present invention relates generally to printing. More particularly, the present invention relates to a continuous process for indirect printing of polymeric films having texture during the formation of the films.
Image graphics are omnipresent in modern life. Images that are used for product identification, marketing purposes, etc., are applied to a variety of surfaces.
The use of ink jet printing to apply such image graphics is desirable. In fact, the use of thermal and piezo ink jet inks has greatly increased in recent years with accelerated development of inexpensive and efficient ink jet printers, ink delivery systems, and the like.
Articles having replicated texture, for example, are used for a variety of purposes. A few examples of such articles, having microreplicated texture in particular, are stemmed webs, and hook and loop fasteners, etc. (See, for examples, U.S. Pat. No. 4,959,265 (Wood et al.), U.S. Pat. No. 5,845,375 (Miller et al.), which may be used for a multitude of purposes. It may be desirable to apply image graphics to these articles.
Currently, images are typically applied to the non-textured side of the articles. The problem with applying graphics to the non-textured side is that the material of the article may not be transparent, which will not allow the graphics to be seen from the textured side of the article. Another problem with printing on the non-textured side is that the ink may not be compatible with the non-textured side or with another coating that is applied to the non-textured side, such as an adhesive.
Images may also be applied to the textured side. The current processes that are known for applying images to the textured side, however, are by using lamination or printing on the surface of a completely formed article. One problem with using the known processes is the lack of durability or abrasion resistance of the image. The image may be easily worn off because the image is printed on the tops of the protrusions that provide the texture.
The inventors recognized that if an image could be printed substantially on the area between protrusions making up the textured side of a thermoplastic film, it would have good abrasion resistance. They also recognized that printing on the area between protrusions on a textured side would provide good resolution of the image. As a result, the inventors, invented a continuous method for indirect printing of an image on a textured side(s) of a thermoplastic film, having texture on at least one side, during the formation of said films.
The inventive method is a method of indirect printing on a thermoplastic film having texture, wherein said method comprises: a) providing a heated thermoplastic melt; b) providing a tool having a molding portion that comprises a texture having a surface and a plurality of cavities in said surface, and that comprises a material having a surface energy sufficient to release ink; c) applying ink to said texture; d) substantially drying or curing said ink; e) contacting said thermoplastic melt with said molding portion having ink applied to it; f) forming a texture in said thermoplastic melt, wherein said texture comprises a plurality of protrusions and an area between said protrusions, that is the inverse of the texture of said molding surface; g) transferring said ink from said molding portion to said thermoplastic melt; h) quenching said thermoplastic melt to form a thermoplastic film; and i) removing said thermoplastic film from said molding portion.
The invention also includes an article, which comprises: a) a thermoplastic film having a texture on at least one side wherein said texture comprises protrusions and an area between said protrusions; and b) ink appearing on at least a portion of said textured side wherein said ink is on less than 10% of the surface area of said protrusions.
An advantage of the present inventive method is that the image, which is different than the pattern of protrusions, appears substantially in the area between the protrusions on the textured side. Therefore, the printed images have good wear resistance. In addition, the printed images also have good resolution.
In the present invention:
xe2x80x9cSurface energyxe2x80x9d means energy being equal to the surface tension of the highest surface tension liquid (real or imaginary) that will completely wet a solid with a contact angle of 0 degrees, which may be determined by measuring the critical surface tension from static contact angles of pure liquids using the methods of W. A. Zisman described in xe2x80x9cRelation of Equilibrium Contact Angle to Liquid and Solid Constitutionxe2x80x9d, ACS Advances in Chemistry #43, American Chemical Society, 1961, pages 1-51.